• History of communications
• Network Models
• Network Hardware
• Network Diagrams

• Distinguish between peer-to-peer and client-server networks

• Identify types of applications and protocols used on a network

• Describe various networking hardware devices

• able to draw network diagrams

• Speed, distance, and cost are the drivers of communications technology

• Approaches to long-distance communications
  • Couriers
  • Telegraphy
  • Computer networks

• Couriers physically transport messages
  • messenger pigeons, pony express, AusPost

• Can overcome great distances, but are slow and costly

• Telegraphs transmit messages using signals
  • drums, beacons, mirrors, smoke, flags, what else (can you think of any)?

• Optical telegraphs were invented inthe 1790s and could propagate signals 800km in 3 minutes

• Optical telegraphs were replaced byelectric telegraph networks
  • Faster and cheaper

• Topology describes how parts of a whole work together
• Physical topology mostly refers to a network’s hardware and how computers, other devices, and cables work together to form the physical network
• Logical topology refers to how software controls access to network resources
  • includes how users and software initially gain access to the network
• network operating system (NOS) controls access to the entire network
  • NOS is required by client-server models

• a peer-to-peer (P2P) network model the OS of each computer on the network is responsible for controlling access to its resources
  • There is no centralised control
• Computers, called nodes or hosts, form a logical group of computers and users
  • Each computer controls its own administration, resources, and security
• Advantages
  • Simple configuration
  • Less expensive compared to other network models
• Disadvantages
  • Not scalable
  • Not necessarily secure
  • Not practical for large installations

• Resources are managed by the NOS via a centralised directory database
• Windows domain is a logical group of computers that a Windows Server can control

• Active Directory (AD) is the centralised directory database that contains user account information and security for the entire group of computers
• user can sign on to the network from any computer on the network and gain access to the resources that AD allows
  • This process is managed by Active Directory Domain Services (AD DS)
• computer making a request from another is called the client

• Figure 1-2  A Windows domain uses the client-server model to control access to the network, where security on each computer or device is controlled by a centralised database on a domain controller

• The NOS is responsible for:
  • Managing client data and other resources
  • Ensuring authorised user access
  • Controlling user file access
  • Restricting user network access
  • Dictating computer communication rules
  • Supplying applications and data files to clients
• Servers that have a NOS installed require:
  • More memory, processing power, and storage capacity
  • Equipped with special hardware to provide network management functions

• Network services are the resources a network makes available to its users
  • includes applications and the data provided by these applications
• client-server applications:
  • client computer requests data or a service from a second computer, called the server

• Figure 1-3 A web browser (client application) requests a web page from a web server (server application); the web server returns the requested data to the client

• Protocols are methods and rules for communication between networked devices
• Two primary network protocols:
  • TCP (Transmission Control Protocol)
  • (Internet Protocol)
• Popular client-server applications include:
  • Web service
  • Email services
  • DNS service
  • FTP service
  • Database services
  • Remote access service

• Figure 1-5 SMTP is used to send email to a recipient’s email server, and POP3 or IMAP4 is used by the client to receive email

• Figure 1-7 This LAN has five computers, a network printer, a local printer, a scanner, and a switch, and uses a star topology

• LAN (local area network) is usually contained in a small space
• switch receives incoming data from one of its ports and redirects it to another port or multiple ports
  • Will send the data to its intended destination
• The physical topology used by this network is called a star topology
  • All devices connect to one central device (usually a switch)
• NIC (network interface card) is a network port used to attach a device to a network
  • Also called a network adapter
• LAN can have several switches
• backbone is a central conduit that connects the segments (pieces) of a network

• Figure 1-11 This local network has three switches and is using a hybrid topology

• router is a device that manages traffic between two or more networks
  • Can help find the best path for traffic to get from one network to another
• Routers can be used in small home networks to connect the home LAN to the Internet
  • Called a SOHO (small office-home office) network
• Industrial-grade routers can have several network ports, one for each network it connects to
• Difference between router and switch:
  • router is like a gateway between networks and belongs to two or more local networks
  • switch belongs only to its local network

• Figure 1-14 (a) A router stands between the LAN and the Internet, connecting the two networks; (b) Home networks often use a combo device that works as both a switch and a router

• WAN (wide area network) is a group of LANs that spread over a wide geographical area
• MAN (metropolitan area network) is a group of connected LANs in the same geographical area
  • Also known as a campus area network (CAN)
• MANs and WANs often use different transmission methods and media than LANs
• PAN (personal area network) is a much smaller network of personal devices
  • network of personal devices such as your smartphone and your computer
• Other network types:
  • BAN (body area network)
  • SAN (storage area network)
  • WLAN (wireless local area network)

• Figure 1-17 A WAN connects two LANS in different geographical areas

• Network diagrams are graphical representations of a network’s devices and connections
  • They may show physical layout, logical topology, IP address reserves, names of major network devices, and types of transmission media
• Network mapping - the process of discovering and identifying the devices on a network
  • Nmap – one of the most popular tools used for network mapping
  • Zenmap – Nmap’s GUI option
• Cisco Systems set the standard for diagram symbols used to represent network devices

• Network diagrams provide broad snapshots of a network’s physical or logical topology
  • Useful for planning where to insert a new switch or determining how a particular router, gateway, or firewall interact
• Wiring schematic is a graphical representation of a network’s wired infrastructure
  • detailed form, it shows every wire necessary to interconnect network devices
• Rack diagram is a drawing that show devices stacked in a rack system

• Tips for labelling and naming conventions:
  • Use names that are as descriptive as possible
  • Only include fields that are essential in identifying the device
  • Don’t overcomplicate the name with useless or redundant information
  • Use established naming conventions
  • Think big-picture-down-to-details

• Tips for labelling and naming conventions:
  • Consider any security risks from details included in your naming convention
  • Use colour-coded cables and use cable tags to identify each cable’s purpose
  • Label the ports and jacks that cables connect to
  • Where labels won’t fit on the device, draw a simple diagram of each device that indicates how each port is used
  • Use labels that are durable and are designed to stick to plastic and metal

• OSI reference model
• Physical transmission
• Safety and troubleshooting network

• Describe the seven layers of the OSI model

• Explain best practices for safety when working with networks and computers

• Describe the seven-step troubleshooting model for troubleshooting network problems

• Explain basic data transmission concepts, including frequency, bandwidth, throughput, multiplexing, and common transmission flaws

• Explain best practices for safety when working with networks and computers

• The application layer describes the interface between two applications, on separate computers
• Application layer protocols are used by programs that fall into two categories:
  • Provide services to a user, such as a browser and Web server
  • Utility programs that provide services to the system, such as SNMP (Simple Network Management Protocol) programs that monitor and gather information about network traffic
• Payload is the data that is passed between applications or utility programs and the OS

• The presentation layer is responsible for reformatting, compressing, and/or encrypting data in a way that the receiving application can read
• Example:
  • email message can be encrypted at the Presentation layer by the email client or by the OS

• The session layer describes how data between applications is synched and recovered if messages don’t arrive intact at the receiving application
• The application, presentation, and session layers are intertwined
  • often difficult to distinguish between them
• Most tasks are performed by the OS when an application makes an API call to the OS
  • API (application programming interface) call is the method an application uses when it makes a request of the OS

• The transport layer is responsible for transporting Application layer payloads from one application to another
• Two main Transport layer protocols are:
  • TCP (Transmission Control Protocol) - makes a connection with the end host, checks whether data was received; called a connection-oriented protocol
  • UDP (User Datagram Protocol) - does not guarantee delivery by first connecting and checking whether data is received; called a connectionless protocol

• Protocols add control information in an area at the beginning of the payload (called header)
• Encapsulation is the process of adding a header to the data inherited from the layer above
• The Transport layer header addresses the receiving application by a number called a port
• a message is too large, TCP divides it into smaller messages called segments
  • UDP, the message is called a datagram

• The network layer is responsible for moving messages from one node to another until they reach the destination host
• The principal protocol used by this layer is IP (Internet Protocol)
• adds its own network layer header to the segment or datagram
  • The entire network layer message is called a packet

• IP address is an address assigned to each node on a network
  • The network layer uses it to uniquely identify each host
• relies on several routing protocols to find the best route for a packet to take to reach destination
  • ICMP and ARP are examples
• Network layer protocol will divide large packets into smaller packets in a process called fragmentation

• Layers 2 and 1 are responsible for interfacing with physical hardware on the local network
  • Protocols at these layers are programmed into firmware of a computer’s NIC and other hardware
• Type of networking hardware or technology used on a network determine the data link layer protocol used
  • Ethernet and Wi-Fi are examples

• The data link layer puts control information in a data link layer header and at the end of the packet in a trailer
  • The entire data link layer message is called a frame
• MAC (Media Access Control) address is also called a physical address, hardware address, or data link layer address
  • embedded on every network adapter

• The physical layer is responsible for sending bits via a wired or wireless transmission
• Bits can be transmitted as:
  • Wavelengths in the air
  • Voltage on a copper wire
  • Light (via fibre-optic cabling)

• Protocol data unit (PDU) is the technical name for a group of bits as it moves from one layer to the next and from one LAN to the next
  • Technicians loosely call this group of bits a message or a transmission

• Transmission techniques in use on today’s network are complex and varied
• This section covers:
  • Measurements that indicate network efficiency
  • Obstacles to good network performance

• Frequency is typically measured in MHz or GHz, which indicates the number of times in a second that an electrical signal can change states
• Bandwidth is the amount of data that could be theoretically transmitted during a given period of time
• Throughput is the measure of how much data is actually transmitted during given time period
• New technologies such as modulation (sending data over an analogue signal) and encoding (converting data into a digital signal for transmission) offer methods for increasing theoretical bandwidth and effective data throughput given the same maximum frequency

• Noise is any undesirable influence degrading or distorting signal
  • Noise is measured in dB (decibels)
• Two common sources of noise include the following:
  • EMI (electromagnetic interference) is caused by motors, power lines, televisions, copiers, fluorescent lights, etc…
    • One type of EMI is RFI (radio frequency interference)
  • Cross-talk occurs when the signal on one wire infringes on adjacent wire signal
    • Alien cross-talk occurs between two cables
    • Near end cross-talk (NEXT) occurs near source
    • Far end cross-talk (FEXT) occurs at the far end

• Attenuation is the loss of a signal’s strength as it travels away from source
• Signals can be boosted using a repeater, which regenerates a digital signal in its original form without noise previously accumulated
• Latency is the delay between signal transmission and receipt
  • Latency may cause network transmission errors
• The length of the cable affects latency, as does the existence of any intervening device

• RTT (round trip time) is the time for packet to go from sender to receiver, then back from receiver to sender
• packets experience varying amounts of delay they can arrive out of order
  • problem commonly called jitter or PDV (packet delay variation)

• NIC settings include the direction in which signals travel over the media and the number of signals that can traverse the media at any given time
  • These two settings are combined to create different methods of communication
• Full-duplex – Signals travel in both directions over a medium simultaneously
• Half-duplex – Signals may travel in both directions but only in one direction at a time
• Simplex – Signals may travel in only one direction and is sometimes called one-way or unidirectional, communication
• Windows, use Device Manager to configure a NIC, including speed and duplex settings

• Multiplexing is a form of transmission that allows multiple signals to travel simultaneously over one medium
• carry multiple signals, the medium’s channel is logically separated into multiple smaller channels, or subchannels
• Multiplexer (mux) is a device that combines many channel signals
  • required at the transmitting end of the channel

• demultiplexer (demux) separates the combined signals on the receiving end
• Three types of multiplexing are used on copper lines:
  • TDM (Time division multiplexing) divides a channel into multiple time intervals
  • STDM (statistical time division multiplexing) assigns slots to nodes according to priority and need
  • FDM (Frequency Division Multiplexing) assigns different frequency band for each communications subchannel

• Three types of multiplexing are used on fiber-optic cable
  • WDM (Wavelength Division Multiplexing) carries multiple light signals simultaneously by dividing a light beam into different wavelengths or colors
  • DWDM (Dense Wavelength Division Multiplexing) increases the number of channels provided by normal WDM
  • CWDM (Coarse Wavelength Division Multiplexing) lowers cost by spacing frequency bands wider apart to allow for cheaper transceiver equipment

• Network and computer technicians need to know how to protect themselves
  • wells as protect sensitive electronic components
• This section takes a look at some best practices for safety

• Know the best escape route or emergency exit
• Fire Suppression Systems - have a fire suppression system in the data center that includes:
  • Emergency alert system
  • Portable fire extinguishers
  • Emergency power-off switch

• Ask yourself: Does the security system allow access during a failure (fail open) or deny access during the failure (fail close)?
• SDS (safety data sheet) explains how to properly handle substances such as chemical solvents and how to dispose of them
  • Includes information such as identification, first-aid measures, fire-fighting measures, accidental release measures, handling and storage guidelines, exposure controls, and physical and chemical properties

• Electrical and tool safety is generally regulated by OSHA (Occupational Safety and Health Administration)
• OSHA guidelines when using power tools:
  • Wear PPE (personal protective equipment)
  • Keep all tools in good condition and properly store tools not in use
  • Use the right tool for the job and operate the tool according to the manufacturer’s instructions
  • Watch out for trip hazards, so you and others don’t stumble on a tool or cord

• Lifting Heavy Objects - follow these guidelines:
  • Decide which side of object to face so load is most balanced
  • Stand close to the object with your feet apart
  • Keep your back straight, bend knees and grip load
  • Lift with your legs, arms, and shoulders (not your back or stomach)
  • Keep the load close to your body and avoid twisting your body while you’re holding it
  • put the object down, keep your back as straight as possible and lower object by bending your knees

• Protecting Against Static Electricity
  • Computer components are grounded inside a computer case
  • Grounding means that a device is connected directly to the earth
• Sensitive electronic components can be damaged by ESD (electrostatic discharge)
• Static electricity can cause two types of damage:
  • Catastrophic failure - destroyed beyond use
  • Upset failure - shorten the life of a component

• Before touching a component, ground yourself by:
  • Wearing an ESD strap around your wrist that clips onto the chassis or computer case
  • Touching the case before touching any component inside the case
  • Storing a component inside an antistatic bag
• addition to protecting against ESD, always shut down and unplug a computer before working inside it

• Troubleshooting steps used by most expert networking troubleshooters:
  1. Identify problem
     • Gather information
     • Identify symptoms
     • Question users
     • Determine if anything has changed
  2. Establish theory of probable cause
     • Question the obvious

• Troubleshooting steps
  3. Test theory to determine cause
     • theory confirmed, determine next steps
     • theory not confirmed, establish new theory or escalate
  4. Establish action plan
  5. Implement solution or escalate the problem
  6. Verify full functionality
     • Implement preventative measures if applicable
  7. Document findings, actions, outcomes

• Network infrastructure
• Types of cables
• Ethernet standards
• Binary calculation

• Describe the roles of various network and cabling equipment in commercial buildings and work areas

• Identify types of cables

• Describe the Ethernet protocol

• Understand how to convert binary

• ANSI/TIA-568 Commercial Building Wiring Standard
  • Also known as structured cabling
• The wiring standard describes the best way to install networking media to maximise performance and minimise upkeep
  • The principles apply no matter what type of media, transmission technology, or networking speeds are involved
• Structured cabling is based on a hierarchical design and assumes a network is based on the star topology

• Entrance Facility in Building A:
  • (entrance facility) – location where the incoming network (such as Internet) connects with the school or corporate network
  • Demarc (demarcation point) – the device that marks where a telecommunications service provider’s network ends and the organisation’s network begins

• Entrance Facility in Building A:
  • MDF (main distribution frame) – the centralised point of interconnection for an organisation’s LAN or WAN (also called MC or main cross connect)
  • Data room – an enclosed space that hold network equipment (also called data closet, data centre, equipment room, or telecommunications room)
  • Rack – holds various network equipment
  • Patch panel – a panel of data receptors which can be mounted to a wall or a rack
    • patch panel provides a central termination point when many patch cables converge in a single location

• Entrance Facility in Building A (continued):
  • VoIP telephone equipment – VoIP (Voice over IP) is the use of any network to carry voice signals using TCP/IP protocols
  • ne or more data rooms you might find the following:
    • VoIP gateway
    • VoIP PBX
    • VoIP endpoints

• Data Room in Building B:
  • IDF (intermediate distribution frame) – provides an intermediate connection between the MDF and end-user equipment on each floor and in each building
• Work Areas in All Three Buildings:
  • Work area – encompasses workstations, printers, and other network devices
  • Wall jacks – the ANSI/TIA standard calls for each wall jack to contain at least one voice and one data outlet

• Rack Systems
  • Racks come in two-post and four-post varieties (though six-post racks are also available)
  • Racks may be wall- or ceiling-mounted, freestanding on the floor, or bolted to the floor
  • Consider the following when purchasing racks:
    • Height – rack height is measured in rack units (RU or U) with the industry standard being 42U tall
    • Width – equipment racks come in a standard 19-inch frame (19 inches wide)
    • Depth – rack depths vary between manufacturers
  • data centres containing multiple rows of racks, a hot aisle/cold aisle layout pulls cool air from vents in the floor or from low-lying wall vents into rows of racks (see Figure 2-14)

• Types of Cables
  • Patch cable – a relatively short length of cabling with connectors at both ends
  • Horizontal cabling – connects workstations to the closest data room and to switches housed in the room
  • Backbone cabling – consists of cables or wireless links that provide interconnection between the entrance facility and MDF and between MDF and IDFs
  • Many network problems are the result of poor cable installations
    • Pay close attention to the quality of cable connections and cable management

• Cable Management
  • Termination – when terminating twisted-pair cabling, don’t leave more than 1 inch of exposed cable before a termination
  • Bend radius – do not exceed the cable’s prescribed bend radius, which is the radius of the maximum arc into which you can loop a cable without impairing data transmission
  • Continuity – use a cable tester to verify that each cable segment transmits data reliably
  • Loosely cinch cables

• Cable Management
  • Cable coverings and conduits – avoid laying cables across a floor and use cord covers if they must be exposed
  • EMI sources – install cable at least 3 feet away from fluorescent lights or other sources of EMI (electromagnetic interference)
  • Plenum cabling – if running cable in the plenum (the area above the ceiling tile or below subflooring), make sure the cable sheath is plenum-rated

• Cable Management (continued)
  • Grounding - pay attention to grounding requirements
  • Slack in cable runs
  • Cable trays - use cable management devices such as cable trays, braided sleeving, and furniture grommets
  • Patch panels - use patch panels to organise and connect lines
  • Company standards and inventory
  • Documentation
    • Keep your cable plant documentation accessible
    • Label every data jack or port, patch panel and connector
    • Use color-coded cables for different purposes
    • Update your documentation as you make changes to the network

• Ethernet is the most important data link layer standard
  • capable of running on a variety of network media
  • Ethernet offers excellent throughput at a reasonable cost
  • the most popular network technology used on modern LANs
• Ethernet II is the current standard
• Ethernet adds both a header and a trailer to the payload
  • This creates a frame around the payload
• The header and FCS make up the 18-byte “frame” around the data
• The data portion of an Ethernet frame may contain from 46 to 1500 bytes
• MTU (maximum transmission unit) is the largest size that routers in a message’s path will allow at the Network Layer

• Logical link Control (LLC) : (IEEE 802.2)
  • The Logical Link Control (LLC) sublayer remains relatively independent of the physical equipment
  • Provides an interface between the MAC layer and the Network layer independent of the hardware

• Media Access Control (MAC): (part of IEEE 802.3)
  • The MAC sub-layer is concerned with the physical components that will be used to communicate the information
  • Which computer can access the network when multiple computers are trying to access it simultaneously
  • Physical addressing (MAC addresses) and access control methods.

• Mbps Ethernet
• Mbps Fast Ethernet
• Gigabit Ethernet
• Gigabit Ethernet

• 10BASE5, 10BASE2, and 10BASE-T Ethernet are now considered Legacy Ethernet

IEEE 802 Committee Standards:

• 1 - Standards introduction
• 2 - Logical Link Control (LLC)
• 3 - Ethernet
• 4 - Token Bus - 75 ohm CATV coax or Fibre
• 5 - Token Ring
• 6 - MAN (Metropolitan Area Network) - similar to FDDI
• 7 - Broadband
• 8 - Fibre Optics
• 9 - Integrated Voice and Data
• 10 - LAN Security
• 11 - Wireless
• 12 - 100 VG AnyLAN
• 15 - Bluetooth
• 16 - WiMax

• Ethernet performs three functions:
  • Transmitting and receiving data frames
    • Uses CSMA/CD (non-deterministic)
    • Carrier Sense Multiple Access / Collision Detection

• Decoding data frames and checking them for valid MAC addresses
  • before passing them to the upper layers of the OSI model

• Detecting errors within data frames or on the network
  • Note that Ethernet performs error detection but NOT error correction
  • Any frame with an incorrect checksum is an error
  • Also, any frame under 64 bytes in length is an error

• Ethernet was originally designed to work on networks with a shared medium
  • physical bus topology
  • star topology created with a hub
• multiple nodes attempt to communicate at the same time, the signals will interfere
  • called a collision
• CSMA/CD is used for controlling access to the shared medium

• Convert 10011101 into decimal

• Convert 10011101 into decimal
• What if we had more than 8 bits?

• Remainder method.

• Checking your answer
  • Make sure you have the correct number of bits
  • Convert back to decimal to check if you converted correctly

• AND
• OR
• NOT
• XOR

• Binary numbers in 60 seconds
  • http://www.youtube.com/watch?v=qdFmSlFojIw

• Binary - So Simple a Computer Can Do It
  • http://www.kerryr.net/pioneers/binary.htm

• Cisco Binary Game
  • http://forums.cisco.com/CertCom/game/binary_game_page.htm

• Layer 1
  • Repeaters, hubs, amplifiers, transceivers
• Layer 2
  • Switches (traditional), bridges
• Layer 3
  • Routers
• NICs function at both layer 1 and 2

• Collision domains are segments of a network where collisions can potentially occur
• Layer 1 devices extend collision domains
• Layer 2 devices break up collision domains

• Nodes on the same LAN exchange data by sending frames
• Each frame contains a source and destination MAC address to define the sender and receiver
• Broadcast frames are received by all devices
• Layer 1 and 2 devices extend broadcast domains
• Layer 3 devices break up broadcast domains

• Switches examine the MAC addresses of frames to determine forwarding decisions
  • Unlike hubs, which simply forward all frames out of ports
• Switches only send frames out of the port which is connected to the destination
  • Hence they break up collision domains
• Switches send broadcast frames out of all ports aside from the port the frame came in
  • Hence they extend broadcast domains

• Switches associate interfaces (ports) to MAC addresses in a bridging table
• The bridging table is empty when a switch is first connected
• When a frame is received on a given interface, the switch associates the source MAC address with that interface
• a switch sees an unknown destination MAC address, it forwards the frame on all ports aside from the source port (“flooding”)

• Store-and-Forward
  • The switch waits until it has received the entire frame and can verify that it’s valid before forwarding
  • Slow, but error free
• Cut through
  • The switch begins forwarding the frame as soon as it sees the destination MAC address
  • Fast, but errors are passed on
• Fragment free
  • The switch waits until it receives the whole frame header before forwarding
  • Slower than cut through, but catches some errors

• your Internet router has hub ports instead of switched ports this is why it slows down when you connect a few extra computers

• Routers are a layer 3 (Network layer) device
• Routers connect networks
• Routers building routing tables to all known destination networks by exchanging their routing tables with adjacent routers.
• Routers select the best path for incoming data packets to reach their destination networks

• address
• DNS
• Addressing issues

• Work with MAC addresses

• Configure TCP/IP settings on a computer, including IP address, subnet mask, default gateway, and DNS servers

• Identify the ports of several common network protocols

• Describe domain names and the name resolution process

• There are four addressing methods:
  • Data link layer MAC (Media Access Control) address is 48 bits, written as six hex numbers separated by colons
    • also called a physical address
    • MAC addresses are embedded on every NIC in the world
  • Network layer IP (Internet Address) address can be used to find any computer in the world
    • IPv4 addresses have 32 bits and are written as four decimal numbers called octets
    • IPv6 addresses have 128 bits and are written as eight blocks of hexadecimal number
  • Transport layer port numbers are used to find applications
  • Application layer FQDNs, computer names, and host names
    • Fully qualified domain name (FQDN) – a unique character-based name

• Traditional MAC addresses contain two parts
  • The first 24 bits are known as the OUI (Organizationally Unique Identifier) or manufacturer-ID
    • This part is assigned by the IEEE
  • The last 24 bits make up the extension identifier or device ID
    • Manufacturer’s assign each NIC a unique device ID
• Switches use MAC addresses to identify devices on the local area network

• Static IP addresses are assigned manually by the network administrator
• Dynamic IP addresses are automatically assigned by a DHCP server
  • You’ll learn more about DHCP later in the chapter
• There are two types of IP addresses:
  • IPv4 is a 32-bit address
  • IPv6 is a 128-bit address

• 32-bit IPv4 address is organized into four groups of 8 bits each (known as octets)
  • Each of the four octets can be any number from 0 to 255
  • Some IP addresses are reserved
• Example of an IPv4 address: 72.56.105.12
• Classful addressing
  • The dividing line between the network and host portions is determined by the numerical range the IP address falls in
• Classful IPv4 addresses are divided into five classes:
  • Class A, Class B, Class C, Class D, and Class E

• Class A, B, and C licensed IP addresses are available for use on the Internet
  • These are called public IP addresses
• company can use private IP addresses on its private networks
• The IANA recommends the following IP addresses be used for private networks:
  • 0.0 through 10.255.255.255
  • 0.0 through 172.31.255.255
  • 0.0 through 192.168.255.255

• Classless addressing allows the dividing line between network and host portions to fall anywhere along the string of binary bits in an IP address
• CIDR (Classless Interdomain Routing) notation takes the network ID or a host’s IP address and follows it with a forward slash (/) followed by the number of bits that are used for the network ID

• Network Address Translation (NAT) is a technique designed to conserve public IP addresses needed by a network
• Address translation is a process where a gateway device substitutes the private IP addresses with its own public address
  • When these computers need access to other networks or Internet
• Port Address Translation (PAT) is the process of assigning a TCP port number to each ongoing session between a local host and Internet host

• Two variations of NAT to be aware of:
  • SNAT (Source Network Address Translation) - the gateway assigns the same public IP address to a host each time it makes a request to access the Internet
  • DNAT (Dynamic Network Address Translation) - the gateway has a pool of public address that it is free to assign to a local host when it makes a request to access the Internet

• IPv6 address has 128 bits written as eight blocks of hexadecimal numbers separated by colons
  • 0000:0B80:0000:0000:00D3:9C5A:00CC
  • Each block is 16 bits
  • Leading zeros in a four-character hex block can be eliminated
  • blocks contain all zeroes, they can be written as double colons (::), only one set of double colons is used in an IP address
  • Therefore, above example can be written two ways:
    • :B80:0000:0000:D3:9C5A:CC
    • B80::D3:9C5A:CC (this is the preferred method because it contains the fewest zeroes)

• IPv6 terminology:
  • link (sometimes called local link) is any LAN bounded by routers
  • Neighbours are two or more nodes on the same link
  • Dual stacked is when a network is configured to use both IPv4 and IPv6
  • Tunnelling is a method used by IPv6 to transport IPv6 packets through or over an IPv4 network
  • Interface ID is the last 64 bits or four blocks of an IPv6 address that identify the interface

• Unicast address - specifies a single node on a network
  • Global address can be routed on the Internet
  • Link local address can be used for communicating with nodes in the same link
  • Loopback address can be used to test that an interface and supporting protocol stack are functioning properly
• Multicast address – delivers packets to all nodes on a network
• Anycast address - can identify multiple destinations, with packets delivered to the closest destination

• IPv6 autoconfiguration
  • IPv6 addressing is designed so that a computer can autoconfigure its own link local IP address
  • This process is called SLAAC (stateless address autoconfiguration)
• Step 1 - The computer creates its IPv6 address
  • uses FE80::/64 as the first 64 bits (called prefix)
  • The last 64 bits are generated from the network adapter’s MAC address
• Step 2 - The computer checks to make sure its IP address is unique on the network
• Step 3 - The computer asks if a router on the network can provide configuration information
  • This message is called an RS (router solicitation) message

• port is a number assigned to a process that can receive data
  • Port numbers ensure data is transmitted to the correct process among multiple processes running on a single device
• socket consists of host’s IP address and the port number of an application running on the host
  • colon separates the two values
  • Example - 10.43.3.87:23
• Port numbers are divided into three types:
  • Well-known ports - 0 to 1023
  • Registered ports - 1024 to 49151
  • Dynamic and private ports - 49152 to 65535

• Character-based names are easier to remember than numeric IP addresses
• URL (uniform resource locator) is an addressing scheme that identifies where to find a particular resource on a network
• Last part of an FQDN is called the top-level domain (TLD)
• Domain names must be registered with an Internet naming authority that works on behalf of ICANN
  • ICANN restricts what type of hosts can be associated with .arpa, .mil, .int, .edu, and .gov
• Name resolution is the process of discovering the IP address of a host when you know the FQDN

• DNS is an Application layer client-server system of computers and databases made up of these elements:
  • Namespace - the entire collection of computer names and their associated IP addresses stored in databases on DNS name servers around the globe
  • Name servers - hold databases, which are organised in a hierarchical structure
  • Resolvers - a DNS client that requests information from DNS name servers

• Each organisation that provides host services is responsible for providing and maintaining its own DNS authoritative servers for public access
  • authoritative name server is the authority on computer names and their IP addresses for computers in their domains
• The domains that the organisation is responsible for managing are called a DNS zone

• Four common types of DNS servers:
  • Primary DNS server – the authoritative name server for the organisation
    • Holds the authoritative DNS database for the organisation’s zones
  • Secondary DNS server – backup authoritative name server for the organisation
  • Caching DNS server – accesses the public DNS data and caches the DNS information it collects
  • Forwarding DNS server – receives queries from local clients but doesn’t work to resolve the queries

• Any of these DNS server types can co-exist on the same machine
• DNS name servers are organised in a hierarchical structure
• the root level, 13 clusters of root DNS servers hold information used to locate top-level domain (TLD) servers

• Ways the resolution process can get more complex:
  • caching server typically is not the same machine as the authoritative server
    • The caching server exists only to resolve names for its own local clients
  • Name servers within a company might not have access to root servers
  • TLD name server might be aware of an intermediate name server rather than the authoritative name server

• Two types of DNS requests:
  • Recursive lookup – a query that demands a resolution or the answer “It can’t be found”
  • Iterative lookup – a query where the local server issues queries to other servers
    • Other servers only provide information if they have it
    • not demand a resolution

• Several types of records, called resource records are kept in a DNS database:
  • SOA (start of authority) record – gives information about the zone
  • (address) record – stores the name-to-address mapping for a host
  • AAAA (address) record – holds the name-to-address mapping, the IP address is an IPv6 type IP address
  • CNAME (canonical Name) record – holds alternative names for a host

• Several types of records, called resource records are kept in a DNS database:
  • PTR (pointer) record – used for reverse lookups
  • (name Server) record – indicates the authoritative name server for a domain
  • (mail exchanger) record – identifies a mail server and is used for email traffic
  • SRV (service) record – identifies the hostname and port of a computer that hosts a specific network services besides email
  • TXT (text) record – holds any type of free-form text

• BIND (Berkeley Internet Name Domain) is the most popular DNS server software
  • Open source - the term for software whose code is publicly available for use and modification
• Microsoft DNS Server is a built-in DNS service in the Windows Server OS
• Windows Server is capable of split-brain or split-horizon deployment, which is used to handle internal clients and external clients

• Command-line tools are a great resource to troubleshoot network problems
• ping (Packet Internet Groper) utility is used to verify that TCP/IP is:
  • Installed
  • Bound to the NIC
  • Configured correctly
  • Communicating with the network
• The ping utility sends out a signal called an echo request to another device (request for a response)
  • The other computer responds in the form of an echo reply
• ICMP (Internet Control Message Protocol) is the protocol used by the echo request/reply to carry error messages and information about the network

• IPv6 networks use a version of ICMP called ICMPv6
  • ping6 – on Linux computers running IPv6, use ping6 to verify whether an IPv6 host is available
  • ping -6 – on Windows computers, use ping with the -6 switch to verify connectivity on IPv6 networks
• For the ping6 and ping -6 commands to work over the Internet, you must have access to the IPv6 Internet

• The ipconfig command shows current TCP/IP addressing and domain name information on a Windows computer
  • Use ipconfig/all to see a more complete summary of TCP/IP addressing information

• Use the ip utility to view and manage TCP/IP settings
• The ip utility is only available on UNIX and Linux systems
• Any ip commands that change the state of a link require elevated privileges
  • This is accomplished by logging in as the root user or by temporarily elevating the current user's privileges with the sudo (superuser do) command
• ifconfig is a similar utility used to view and manage TCP/IP settings
• your Linux or UNIX system provides a GUI
  • Open a shell prompt, then type ifconfig

• The nslookup (name space lookup) utility allows you to query the DNS database from any computer on a network
  • find the host name of a device by specifying its IP address, or vice versa
  • useful for verifying a host is configured correctly or for troubleshooting DNS resolution problems
• Reverse DNS lookup - to find the host name of a device whose IP address you know
  • nslookup 69.23.208.74

• The nslookup utility is available in two modes:
  • Interactive - to test multiple DNS servers at one time
  • Noninteractive - test a single DNS server
• You can change DNS servers from within interactive mode with the server subcommand and specifying the IP address of the new DNS server
• exit nslookup’s interactive mode, enter exit

• The dig (domain information groper) utility is available on Linux and macOS
  • Provides more detailed information than nslookup and uses more reliable sources of information to output its results
• Use dig to query DNS nameservers for information about host addresses and other DNS records
• IP scanner can be used to gather information about all devices connected to a network

• Incorrect time
  • Check a domain computer’s time source from a Command Prompt window by entering w32tm /query /source
• DHCP Issues
  • you are getting DHCP errors or if multiple clients are having trouble connecting to the network, try the following:
    • Check the settings on your DHCP server
    • Make sure the DHCP scope is large enough to account for the number of clients the network must support
  • Consider implementing a shorter lease time on larger networks

• Network Connection Configuration Issues
  • Common configuration errors:
    • Incorrect IP address
    • Duplicate IP address
    • Incorrect subnet mask
    • Incorrect gateway
    • Incorrect DNS or DNS issues
  • When a computer is struggling to establish a network connection
    • Check its TCP/IP configuration settings
  • the computer is not obtaining an IP address and related information from a DHCP server
    • Static settings might be using the wrong information
    • Try switching to DHCP